1. Field of the Invention
The present invention relates to a method for producing a complex of metallic nanoparticles and inorganic clay and an organic promoter, and particularly to a method using ethanolamine as the organic promoter.
2. Related Prior Arts
It is known that silver nanoparticles (hereinafter abbreviated as AgNPs) are very effective in disinfection for six hundred kinds of bacteria. The AgNPs have higher specific areas than other metallic particles and thus more effective. The AgNPs are lower in toxicity and therefore suitable for massively-produced medicine.
Currently, the AgNPs can be produced by physical processes or chemical processes. For the physical processes, expensive pieces of equipment are usually needed to achieve high vacuum or electron beams. For the chemical processes including redox reactions, reducing agents for reducing silver ions into silver atoms are needed. The reducing agents can be sodium borohydride (NaBH4), formaldehyde, ethanol, or hydrazine (H2N—NH2).
To control particle sizes, stabilizers such as sodium citrate, glucose, sodium dodecyl sulfate (SDS), polyvinylpyrrolidone (PVP) and dendrimer, can be added.
Particularly, concentrations of the silver ions have to be controlled in ppm ranges to avoid aggregation which will impair effects of the product. To solve this problem, continuous blending at a high temperature is required and organic solvents or surfactants are added. However, the organic solvents or surfactants may react with AgNPs to decrease surface areas thereof and result in environmental pollutions. Such processes are also difficult to operate and usually take a long time which will raise the costs.
In addition, dispersants or protective agents are usually added to improve stability and avoid aggregation through electrostatic rejection or steric hindrance. The dispersants can be water soluble polymers, for example, polyvinylpyrrolidone (PVP), polyvinylalcohol (PVA), polymethylvinylether, poly(acrylic acid) (PAA), nonionic surfactants, chelating agents, etc. Inorganic silicates, for example, natural layered clay, can also be used as inorganic dispersants to attract the silver nanoparticles to form complexes.
To improve the conventional processes, the present invention provides a method which is highly efficient and can be operated at lower temperatures.